JP2003249895A - Logarithmic conversion circuit, optical detection circuit, and optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical detection circuit which can detect an accurate optical power, even when a logarithmic amplifier having poor input/output characteristics is used. <P>SOLUTION: An optical detection circuit 10 is provided with a photodiode 11, a current-voltage conversion circuit 12, a logarithmic amplifier 13, an attenuator 14, a logarithmic amplifier 15, and an adder 16. The photodiode 11 outputs a current value corresponding to a received light amount. The current-voltage conversion circuit 12 outputs a voltage value V<SB>0</SB>corresponding to the current value. The logarithmic amplifier 13 outputs a first voltage value V<SB>1</SB>, indicating a logarithmic value of the voltage value V<SB>0</SB>outputted from the current-voltage conversion circuit 12. The attenuator 14 outputs an intermediate voltage value V, obtained by attenuating the voltage value V<SB>0</SB>outputted from the current- voltage conversion circuit 12 by a fixed ratio A. The logarithmic amplifier 15 outputs a second voltage value V<SB>2</SB>, indicating the logarithmic value of the intermediate voltage value V. The adder 16 outputs a voltage value V<SB>3</SB>, indicating the sum of the first voltage value V<SB>1</SB>and the second voltage value V<SB>2</SB>. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a logarithmic conversion circuit that outputs an output voltage value representing a logarithmic value of an input voltage value, a photodetection circuit including the logarithmic conversion circuit and a photodiode, and the photodetection circuit. The present invention relates to an optical amplifier including.

[0002]

2. Description of the Related Art The power of light is the
-Can be detected by a photo-detection circuit comprising a voltage conversion circuit and a log amp. In this photodetector circuit, a current value is output from a photodiode that receives light, the current value is converted to a voltage value by a current-voltage conversion circuit, and the voltage value is converted to a logarithmic value by a log amp, and the A voltage value representing a logarithmic value is obtained as the received light power. The optical power obtained by this photo detection circuit is expressed in dB. The photodetector circuit having such a log amplifier has an advantage that the dynamic range of detectable optical power is large.

In an optical amplifier including such an optical detection circuit, a part of the signal light input to the optical amplification medium is branched and detected by the optical detection circuit to obtain the input signal light power, and the optical amplification medium is obtained. A part of the signal light that is optically amplified and output is branched by and is detected by another photodetector circuit to obtain the output signal light power. Then, the difference between the output signal light power and the input signal light power (that is, the gain of the signal light amplification in the light amplification medium) is obtained, and the excitation of the light amplification medium is controlled so that this difference becomes constant (for example, Reference "JC van der Plaats, et al.," Dynamic Pump-Lo
ss ControlledGain-Locking System For Erbium-Doped
Fiber Amplifiers In Multi-Wavelength Networks ", EC
OC'97, Vol.3, No.127 (1997) ").

[0004]

A log amplifier that can be used in the above photodetection circuit is, for example, Burr-Bro.
The product "LOG100" manufactured by wn and the product "AD8307" manufactured by Analog Devices are known. Comparing the two products, the product “LOG100” has excellent input / output characteristics, but has a drawback that the power supply voltage value is ± 15V. That is, when the power supply voltage value is large, the scale of the power supply circuit for generating the voltage is large, or the power consumption is large.

On the other hand, the product "AD8307" is preferable in that the power supply voltage value is 5 V, but the input / output characteristics are inferior.
Cannot output accurate logarithmic value. A photodetector circuit including a log amplifier that cannot output such an accurate logarithmic value cannot detect an accurate optical power. Moreover, an optical amplifier including such a photodetector circuit cannot perform accurate control.

The present invention has been made in order to solve the above problems, and a logarithmic conversion circuit capable of outputting an accurate logarithmic value even when a log amplifier having inferior input / output characteristics is used, and an accurate light output. An object of the present invention is to provide an optical detection circuit capable of detecting power and an optical amplifier capable of performing accurate control.

[0007]

A logarithmic conversion circuit according to the present invention is a logarithmic conversion circuit which receives an input voltage value and outputs an output voltage value representing a logarithmic value of the input voltage value.
(1) A first log amplifier that inputs an input voltage value or a voltage value proportional thereto and outputs a first voltage value that represents the logarithmic value of the input voltage value; and (2) from an input voltage value adjusting means. Input a voltage value that is output and is proportional to the input voltage value,
A second log amplifier that outputs a second voltage value that represents the logarithmic value of the input voltage value, and (3) the input voltage that makes the voltage values input to the first log amplifier and the second log amplifier different from each other. And (4) inputting the first voltage value output from the first log amplifier and the second voltage value output from the second log amplifier to input the first voltage value and the second voltage value. And an adder that outputs a voltage value representing the sum of the voltage values as an output voltage value.

In the logarithmic conversion circuit according to the present invention, the input voltage value to be logarithmically converted or the voltage value proportional thereto is
It is input to the first log amplifier and logarithmically converted to the first voltage value, and is also input to the second log amplifier and logarithmically converted to the second voltage value. The first voltage value output from the first log amplifier and the second voltage value output from the second log amplifier are added by an adder, and the voltage value representing the sum as the addition result is output from the adder. To be done. The voltage value output from this adder represents the logarithmic value of the input voltage value. In the present invention, the voltage values input to the first log amplifier and the second log amplifier are different from each other by the input voltage value adjusting means. Thereby, the first log amp and the second log amp
The logarithmic conversion errors in the log amps cancel each other out, and the overall logarithmic conversion error of the logarithmic conversion circuit is reduced.

Incidentally, as an input voltage value adjusting means, in front of either one of the first log amplifier and the second log amplifier,
An attenuator or amplifier that multiplies the input voltage value by A (where A ≠ 1) is provided. Alternatively, an attenuator or an amplifier that multiplies the input voltage value by A ₁ is provided in the front stage of the first log amplifier, and an attenuator that multiplies the input voltage value by A ₂ (where A ₁ ≠ A ₂ ) in the front stage of the second log amplifier. Alternatively, an amplifier is provided.

The photodetector circuit according to the present invention inputs (1) a photodiode which outputs a current value corresponding to the amount of received light, and (2) a current value which is output from the photodiode, and outputs the current value according to the current value. Current-voltage conversion circuit that outputs a fixed voltage value,
(3) A logarithmic conversion circuit according to the present invention, which inputs the voltage value output from the current-voltage conversion circuit and outputs an output voltage value representing the logarithmic value of this voltage value. .

In the photodetector circuit according to the present invention, a current value corresponding to the amount of received light is output from the photodiode, and a voltage value corresponding to this current value is output from the current-voltage conversion circuit. Then, the voltage value output from the current-voltage conversion circuit is input to the logarithmic conversion circuit according to the present invention,
An output voltage value representing the logarithmic value of this voltage value is output from the logarithmic conversion circuit. Since this photodetector circuit includes the logarithmic conversion circuit according to the present invention, it is possible to accurately output the voltage value representing the logarithmic value of the amount of light received by the photodiode.

The optical amplifier according to the present invention comprises (1) an optical amplification medium for optically amplifying signal light, and (2) an optical branching device for branching and extracting a part of the signal light input to or output from the optical amplification medium. ,
(3) The photodetector circuit according to the present invention which receives the signal light extracted from the optical branching device and outputs a voltage value according to the amount of received light, and (4) the voltage value output from the photodetector circuit. And a pumping section for pumping the optical amplification medium. In this optical amplifier, the signal light is optically amplified in the optical amplification medium pumped by the pumping unit.
Part of the signal light input to or output from this optical amplification medium is
The light is branched and taken out by the optical branching device, received by the photodetector circuit according to the present invention, and a voltage value corresponding to the amount of received light is output from the photodetector circuit. Then, the excitation of the optical amplification medium by the excitation unit is controlled based on the voltage value output from the photodetection circuit. Since this optical amplifier includes the above-described photodetector circuit according to the present invention, desired control can be accurately performed.

The optical amplifier according to the present invention comprises (1) an optical amplifying medium for optically amplifying the signal light, and (2) a first optical branching device for branching and extracting a part of the signal light input to the optical amplifying medium. , (3) The second optical branching device for branching and extracting a part of the signal light output from the optical amplifying medium, and (4) receiving the signal light extracted by the first optical branching device, A first photodetector circuit that is a photodetector circuit according to the present invention that outputs a corresponding voltage value;
(5) A second photodetector circuit, which is the photodetector circuit according to the present invention, which receives the signal light extracted from the second optical branching device and outputs a voltage value according to the amount of received light. And a pumping section that is controlled based on the difference between the voltage values output from the first photodetector circuit and the second photodetector and that pumps the optical amplification medium. In this optical amplifier, the signal light is optically amplified in the optical amplification medium pumped by the pumping unit. Part of the signal light input to this optical amplification medium is
The light is branched and taken out by the first light branching device, received by the first light detecting circuit, and a voltage value corresponding to the received light amount is output from the first light detecting circuit. Further, a part of the signal light output from this optical amplification medium is branched and taken out by the second optical branching device, received by the second photodetector circuit,
A voltage value according to the amount of received light is output from the second photodetector circuit. Then, based on the difference between the voltage values output from the first photodetector circuit and the second photodetector circuit,
Excitation of the optical amplification medium by the excitation unit is controlled. Since this optical amplifier includes the first photodetector circuit and the second photodetector circuit which are the photodetector circuits according to the present invention, the constant gain control can be accurately performed.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, a logarithmic conversion circuit and an optical circuit according to the present invention.
An embodiment of the detection circuit will be described. Figure 1
It is a block diagram of the photon detection circuit 10 which concerns on a form. Shown in this figure
The light detection circuit 10 includes a photodiode 11, a current
-Voltage conversion circuit 12, log amplifier 13, attenuator 1
4, a log amplifier 15 and an adder 16 are provided. F
The photodiode 11 receives the light whose power is to be detected.
Then, the current value corresponding to the received light amount is output. current voltage
The conversion circuit 12 outputs from the photodiode 11.
Input the current value and the voltage value V according to this current value₀Out
Force Log amp 13, attenuator 14, log un
The input voltage value V ₀Logarithmic value of
Output voltage value V₃According to the present embodiment, which outputs
The conversion circuit 19 is configured.

The log amplifier 13 is a current-voltage conversion circuit 1
The voltage value V ₀ output from 2 is input, and this voltage value V ₀
The first voltage value V ₁ representing the logarithmic value of is output. The attenuator 14 receives the voltage value V ₀ output from the current-voltage conversion circuit 12 and outputs an intermediate voltage value V (= AV ₀ ) obtained by attenuating the voltage value V ₀ with a constant ratio A. Log amp 15
Is the second voltage value V that represents the logarithmic value of this intermediate voltage value V by inputting the intermediate voltage value V output from the attenuator 14.
Output ₂ The adder 16 inputs the first voltage value V ₁ output from the log amplifier 13 and the second voltage value V ₂ output from the log amplifier 15 to input the first voltage value V ₁ and the first voltage value V ₁ voltage value V ₃ representing the sum of the second voltage value V ₂
Is output.

Between the input voltage value V ₀ and the output voltage value V ₁ in the log amplifier 13, there is a relational expression of V ₁ = V _y log (V ₀ / V _x ) ... (1), and the log amplifier 15 There is a relational expression between the input voltage value V and the output voltage value V ₂ at V ₂ = V _y log (V / V _x ) = V _y log (AV ₀ / V _x ) ... (2). The voltage value V ₃ output from the photodetector circuit 10 is expressed by the following equation: V ₃ = B (V ₁ + V ₂ ) ... (3) However, V _y represents a slope, V _x represents an intercept voltage, and each of A and B is a constant. The logarithmic conversion characteristic of the log amplifier 13 and the logarithmic conversion characteristic of the log amplifier 15 are not always good, and they do not have to be good in the present embodiment.

FIG. 2 is a block diagram of a photodetector circuit 20 of a comparative example. The photodetector circuit 20 shown in this figure includes a photodiode 21, a current-voltage conversion circuit 22, and a log amplifier 23. The photodiode 21 receives light whose power is to be detected, and outputs a current value according to the amount of received light. The current-voltage conversion circuit 22 inputs the current value output from the photodiode 21 and outputs a voltage value V ₀ according to this current value. The log amp 23 has a current-
The voltage value V ₀ output from the voltage conversion circuit 22 is input, and the voltage value V ₁ representing the logarithmic value of this voltage value V ₀ is output. The voltage value V ₁ output from the photodetector circuit 20 is expressed by the above equation (1).

Next, the input / output characteristics of the photodetector circuit 10 according to this embodiment and the photodetector circuit 20 of the comparative example will be described. Here, as the log amplifiers 13, 15 and 23, the product “AD8” from Analog Devices is used.
307 "was used. FIG. 3 is a graph showing the input / output characteristics of the photodetector circuit 10 according to this embodiment. In the same figure (a), the relationship between each of the voltage values V ₁ , V ₂ and V ₃ and the received light power is shown. In the figure (b), the errors δV ₁ , δV ₂ , δ of the voltage values V ₁ , V ₂ and V _3, respectively.
The relationship between V ₃ and the received light power is shown. Figure 4 is a graph showing the input-output characteristics of the light detection circuit 20 of the comparative example, the relationship between the voltage value V ₁ and the light-receiving power, and, the relationship between the error .DELTA.V ₁ and the light receiving power of the voltage value V ₁ shows Has been done.
The error is the difference between the output voltage value in the ideal case in which the input / output characteristics are expressed by the logarithmic expression as in the above equation (1) and the actually measured output voltage value.

As shown in FIG. 4, in the photodetector circuit 20 of the comparative example, the error δV ₁ of the output voltage value V ₁ periodically fluctuates as the received light power increases. Further, as shown in FIG. 3, also in the photodetector circuit 10 of the present embodiment, the errors δV ₁ and δV ₂ of the output voltage values of the log amplifiers 13 and 14 are
It fluctuates periodically as the received light power increases. However, the error δV ₃ of the output voltage value V ₃ from the adder 16 of the photodetector circuit 10 of this embodiment is a substantially constant value regardless of the received light power. This is because the attenuator 14 is provided in the preceding stage of the log amp 15, so that the input voltage values to the two log amps 13 and 15 are different, and the logarithmic conversion errors in the log amps 13 and 15 cancel each other out. Because it is done.

Next, an embodiment of the optical amplifier according to the present invention will be described. FIG. 5 shows an optical amplifier 1 according to this embodiment.
It is a block diagram of 00. The optical amplifier 100 shown in this figure
Light-amplifies the signal light input to the input port 101 in the optical amplification fiber 150, and outputs the light-amplified signal light from the output port 102. The optical amplifier 100 includes an optical branching device 140, an optical amplification fiber 150, and an optical multiplexer / demultiplexer 16 between an input port 101 and an output port 102 in this order.
0 and the optical branching device 170 are provided, and the optical branching device 1
The first photodetector circuit 110 is connected to 40, the pump unit 130 is connected to the optical multiplexer / demultiplexer 160, and the optical branching device 1
The second photodetector circuit 120 is connected to 70.

The optical branching device 140 branches a part of the signal light from the input port 101 toward the optical amplification fiber 150 and extracts the signal light, and the extracted signal light is detected by the photodetector circuit 110.
It outputs to the photodiode 111 of. The optical amplification fiber 150 is a silica-based optical fiber in which a rare earth element (Er element, Tm element, or the like) is added to the core region, and serves as an optical amplification medium that optically amplifies the signal light when pumping light is supplied. To work. For example, if the wavelength range of the signal light is the 1.55 μm band, the optical amplification fiber 150 doped with Er element is used, and the wavelength of the pumping light is 1.48.
μm or 0.98 μm. The optical multiplexer / demultiplexer 160 is
The signal light optically amplified by the optical amplification fiber 150 is passed toward the optical branching device 170, and the pumping section 13
The pumping light reaching from 0 is supplied to the optical amplification fiber 150. The optical branching device 170 branches a part of the signal light traveling from the optical amplification fiber 150 through the optical multiplexer / demultiplexer 160 to the output port 102 and takes out the signal light, and outputs the taken out signal light to the photodiode 121 of the photodetector circuit 120. To output.

The first photodetector circuit 110 includes a photodiode 111, a current-voltage conversion circuit 112, and a log amp 11.
3, an attenuator 114, a log amplifier 115, and an adder 116, and has the same configuration as the photodetection circuit 10 (FIG. 1) according to the present embodiment described above. The photodetector circuit 110 receives the signal light extracted from the optical branching device 140 and outputs a voltage value V _in according to the amount of received light. The output voltage value V _in from the photodetector circuit 110 indicates a value obtained by logarithmically converting the power of the signal light input to the input port 101.

The second photodetector circuit 120 includes a photodiode 121, a current-voltage conversion circuit 122, and a log amp 12.
3, an attenuator 124, a log amplifier 125, and an adder 126, and has the same configuration as the photodetector circuit 10 (FIG. 1) according to the present embodiment described above. The photodetector circuit 120 receives the signal light extracted from the optical branching device 170 and outputs a voltage value V _out according to the amount of received light. Output voltage value V from this photodetector circuit 120
_out represents a value obtained by logarithmically converting the power of the signal light output from the output port 102.

The excitation unit 130 includes an excitation light source 131 and a drive circuit.
A path 132, a comparator 133 and a differencer 134.
It The differencer 134 outputs the first photodetector circuit 110.
Voltage value V_inAnd the second photodetector circuit 1
The voltage value V output from 20 _outAlso enter the voltage value
V_outTo the voltage value V_inVoltage value ΔV representing the value obtained by subtracting
Is output. The voltage value Δ output from the difference unit 134
V is the gain of signal light amplification in the optical amplification fiber 150.
It represents a profit. Comparator 133 is differentiator 134
Input the voltage value ΔV output from the
The value of is also input and is actually detected as the voltage value ΔV.
A signal that compares the detection gain with the target gain and shows the comparison result.
Signal to the drive circuit 132. The drive circuit 132 has a ratio
Input the signal showing the result of comparison in the comparator 133,
Drive current supplied to the excitation light source 131 based on the signal of
Adjust the size of. The excitation light source 131 is, for example, a semiconductor
It is a laser light source and is driven by the drive circuit 132.
It is driven by an electric current and outputs excitation light.

The optical amplifier 100 according to this embodiment operates as follows. The pumping light output from the pumping light source 131 is supplied to the optical amplification fiber 150 via the optical multiplexer / demultiplexer 160. The signal light input to the input port 101 enters the optical amplification fiber 150 via the optical branching device 140,
The light is amplified while propagating through the optical amplification fiber 150.
The signal light thus optically amplified is output from the output port 102 via the optical multiplexer / demultiplexer 160 and the optical branching device 170.

A part of the signal light input to the input port 101 is branched and taken out by the optical branching device 140, and is received by the photodiode 111 of the photodetector circuit 110. A current value according to the power of the signal light received by the photodiode 111 is output from the photodiode 111, and the current value is converted into a voltage value by the current-voltage conversion circuit 112. The voltage value output from the current-voltage conversion circuit 112 is logarithmically converted by the log amplifier 113 as it is, and is also logarithmically converted by the log amplifier 115 after being multiplied by A (A ≠ 1) by the attenuator 114. The voltage values logarithmically converted and output by the log amplifiers 113 and 115 are added by the adder 116.
Is added and the voltage value V _in representing the added value is output from the adder 116. The output voltage value V _in from the photodetector circuit 110 indicates the power of the signal light input to the input port 101 in dB.

Optical multiplexer / demultiplexer 1 from optical amplification fiber 150
A part of the signal light traveling toward the output port 102 via 60 is
The light is branched and taken out by the optical branching device 170, and is received by the photodiode 121 of the light detection circuit 120.
A current value according to the power of the signal light received by the photodiode 121 is output from the photodiode 121, and the current value is converted into a voltage value by the current-voltage conversion circuit 122. The voltage value output from the current-voltage conversion circuit 122 is logarithmically converted by the log amplifier 123 as it is and is multiplied by A (A) by the attenuator 124.
After being set to 1), logarithmic conversion is performed by the log amplifier 125. Then, the voltage values logarithmically converted and output by the log amplifiers 123 and 125 are added by the adder 126, and the voltage value V _out representing the added value is added by the adder 1.
It is output from 26. The output voltage value V _out from the photo detection circuit 120 indicates the power of the signal light output from the output port 102 in dB.

Then, the voltage difference V _out output from the second photodetector circuit 120 is output by the differentiator 134 of the excitation unit 130.
From the voltage value V _in output from the first photodetector circuit 110
Is subtracted, and a voltage value ΔV representing the value of the difference (that is, gain) is output. The voltage value ΔV output from the difference unit 134 is input to the comparator 133, and in the comparator 133, the detection gain actually detected as the voltage value ΔV and the target gain are compared. Based on the comparison result, the magnitude of the current supplied from the drive circuit 132 to the excitation light source 131 is controlled. That is, in this optical amplifier 100, the power of the pumping light supplied to the optical amplification fiber 150 is controlled so that the gain of signal light amplification in the optical amplification fiber 150 becomes the target gain.

FIG. 6 is a block diagram of an optical amplifier 200 of a comparative example. The optical amplifier 200 shown in this figure optically amplifies the signal light input to the input port 201 in the optical amplification fiber 250, and outputs the optically amplified signal light to the output port 2
Output from 02. The optical amplifier 200 has an input port 20.
1 and the output port 202 between the optical splitter 240,
An optical amplification fiber 250, an optical multiplexer / demultiplexer 260, and an optical branching device 270 are provided, and the optical branching device 240 has a first
The photodetector circuit 210 is connected, the pump unit 230 is connected to the optical multiplexer / demultiplexer 260, and the optical branching device 270 is connected to the second unit.
The photodetector circuit 220 is connected. The optical amplifier 200 of this comparative example has the same configuration as that of the photodetector circuit 20 (FIG. 2) of the comparative example in each of the photodetector circuits 210 and 220 (FIG. 5). ) Configuration is different. Excitation unit 2 of optical amplifier 200 of comparative example
Reference numeral 30 denotes the pump unit 13 of the optical amplifier 100 according to the present embodiment.
It has the same configuration as 0.

Next, the gain characteristics of the optical amplifier 100 according to the present embodiment and the optical amplifier 200 of the comparative example will be described. Again, as each log amp, Analog De
The product "AD8307" from vices was used. Each of the optical amplifiers 100 and 200 was controlled so that the gain was constant. FIG. 7 is a graph showing the relationship between the input signal light power and the gain in the optical amplifier 100 according to this embodiment. FIG. 8 is a graph showing the relationship between the input signal light power and the gain in the optical amplifier 200 of the comparative example.

As shown in FIG. 8, in the optical amplifier 200 of the comparative example, the gain fluctuates depending on the input signal light power, although the gain is controlled to be constant. This variation in gain is caused by the periodic variation in the logarithmic conversion error of each log amplifier with respect to the increase in the received light power.

In comparison with this, as shown in FIG.
In the optical amplifier 100 of the present embodiment, the gain is controlled to be constant, so that the gain is stable regardless of the input signal light power. This gain stabilization is achieved by providing the attenuator 114 in front of the log amplifier 115 in the first photodetector circuit 110 so that the two log amplifiers 113,
This is because the input voltage values to the respective 115 become different, and the logarithmic conversion errors in the log amplifiers 113 and 115 cancel each other out. Further, in the second photodetector circuit 120, since the attenuator 124 is provided in the preceding stage of the log amplifier 125, the input voltage value to each of the two log amplifiers 123 and 125 becomes different, and the log amplifiers 123 and 125 respectively. This is because the logarithmic conversion errors in are canceled by each other.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, the optical amplifier 100 according to the above-described embodiment detects both the input signal light power and the output signal light power and performs constant gain control, but the present invention is not limited to this. For example, the optical detection circuit according to the present embodiment may be used to detect the output signal light power in an optical amplifier that detects the output signal light power and performs constant output control. Further, in the optical amplifier that detects the input signal light power and feed-forward controls the gain or the output signal light power, the photodetector circuit according to the present embodiment may be used to detect the input signal light power. Furthermore, the photodetector circuit and the logarithmic conversion circuit according to the present embodiment are not limited to being applied to an optical amplifier, but can be applied to a measuring instrument that measures the power of light and an optical monitoring system.

[0035]

As described above in detail, in the logarithmic conversion circuit according to the present invention, the input voltage value to be logarithmically converted or the voltage value proportional thereto is input to the first log amplifier and then supplied to the first voltage amplifier. The value is logarithmically converted and is also input to the second log amp to be logarithmically converted into a second voltage value. The first voltage value output from the first log amplifier and the second voltage value output from the second log amplifier are added by an adder,
A voltage value representing the sum as the addition result is output from the adder. The voltage value output from this adder represents the logarithmic value of the input voltage value. In the present invention, the voltage values input to the first log amplifier and the second log amplifier are different from each other by the input voltage value adjusting means. As a result, the logarithmic conversion errors in the first log amplifier and the second log amplifier are canceled by each other, and the logarithmic conversion error of the entire logarithmic conversion circuit is reduced. Therefore, the logarithmic conversion circuit can output an accurate logarithmic value even when the first log amplifier and the second log amplifier having poor input / output characteristics are used. Further, since the photodetector circuit according to the present invention includes such a logarithmic conversion circuit, it is possible to accurately detect the optical power. Further, since the optical amplifier according to the present invention includes such a photodetector circuit, accurate control can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a photodetector circuit 10 according to the present embodiment.

FIG. 2 is a configuration diagram of a photodetector circuit 20 of a comparative example.

FIG. 3 is a graph showing the input / output characteristics of the photodetector circuit 10 according to this embodiment.

FIG. 4 is a graph showing input / output characteristics of a photodetector circuit 20 of a comparative example.

FIG. 5 is a configuration diagram of an optical amplifier 100 according to the present embodiment.

FIG. 6 is a configuration diagram of an optical amplifier 200 of a comparative example.

FIG. 7 is a graph showing the relationship between input signal light power and gain in the optical amplifier 100 according to the present embodiment.

FIG. 8 is a graph showing the relationship between the input signal light power and the gain in the optical amplifier 200 of the comparative example.

[Explanation of symbols]

10 ... 1st photodetection circuit, 11 ... Photodiode, 12
... current-voltage conversion circuit, 13 ... log amplifier, 14 ... attenuator, 15 ... log amplifier, 16 ... adder, 19 ... logarithmic conversion circuit, 100 ... optical amplifier, 101 ... input port,
102 ... Output port, 110 ... Photodetection circuit, 111 ... Photodiode, 112 ... Current-voltage conversion circuit, 113
... log amplifier, 114 ... attenuator, 115 ... log amplifier, 116 ... adder, 120 ... photodetector circuit, 121 ...
Photodiode, 122 ... Current-voltage conversion circuit, 12
3 ... Log amplifier, 124 ... Attenuator, 125 ... Log amplifier, 126 ... Adder, 130 ... Excitation part, 131 ... Excitation light source, 132 ... Drive circuit, 133 ... Comparator, 134 ...
Difference device, 140 ... Optical branching device, 150 ... Optical amplification fiber, 160 ... Optical multiplexer / demultiplexer, 170 ... Optical branching device.

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) H04B 10/06 10/14 10/26 10/28

Claims (4)

[Claims] 1. A logarithmic conversion circuit which inputs an input voltage value and outputs an output voltage value representing a logarithmic value of the input voltage value, wherein the input voltage value or a voltage value proportional thereto is input. A first log amp that outputs a first voltage value that represents the logarithmic value of the input voltage value; and a voltage value that is output from the input voltage value adjusting means and that is proportional to the input voltage value. A second log amplifier that outputs a second voltage value representing a logarithmic value of the value; and the input voltage value adjusting means that makes the voltage values input to the first log amplifier and the second log amplifier different from each other, respectively. The first voltage value output from the first log amplifier is input, and the second voltage value output from the second log amplifier is input to calculate the sum of the first voltage value and the second voltage value. The voltage value that represents the output voltage value Logarithmic converter characterized in that it comprises an adder which to output. 2. A photodiode that outputs a current value according to the amount of received light, and a current-voltage conversion circuit that inputs the current value output from the photodiode and outputs a voltage value according to this current value. The light detection circuit according to claim 1, further comprising: a logarithmic conversion circuit that receives a voltage value output from the current-voltage conversion circuit and outputs an output voltage value representing a logarithmic value of the voltage value. circuit. 3. An optical amplification medium for optically amplifying signal light, an optical branching device for branching and extracting a part of the signal light input to or output from the optical amplification medium, and a signal light extracted by the optical branching device. The photodetector circuit according to claim 2, which receives the light, and outputs a voltage value according to the amount of the received light, and an excitation unit which is controlled based on the voltage value output from the photodetector circuit and excites the optical amplification medium. An optical amplifier comprising: 4. An optical amplification medium for optically amplifying signal light, a first optical branching device for branching out a part of the signal light input to the optical amplification medium, and a signal light output from the optical amplification medium. A second optical branching device for branching and extracting a part of the signal light; and a light detection circuit according to claim 2, which receives the signal light extracted from the first optical branching device and outputs a voltage value according to the received light amount. The second photodetector circuit according to claim 2, which receives the signal light extracted from the second optical branching device and outputs a voltage value corresponding to the received light amount. An optical amplifier comprising: a circuit; and a pumping section that is controlled based on a difference between voltage values output from the first photodetector circuit and the second photodetector and that pumps the optical amplification medium. .